1. Field of the Invention
The present invention relates to a method and apparatus for providing a high velocity liquid jet for cutting, and more particularly to means for improving the collimation of the liquid jet for improved cutting action.
2. Brief Description of the Prior Art
The use of liquid jets as a means of cutting, drilling, or abrading various materials has long been known. For example, there is the practice of hydraulic mining, where a high pressure liquid jet is used to cut through rock formations, coal formations or the like. Representative of the prior art in this field are the following patents: Kirschniok, U.S. Pat. No. 878,208; Haag, U.S. Pat. No. 1,530,768; Howell, U.S. Pat. No. 1,856,836; Schroepfer, U.S. Pat. No. 2,018,926; Bigelow, U.S. Pat. No. 2,304,143; Aston et al., U.S. Pat. No. 2,518,591; Lindbergh et al., U.S. Pat. No. 3,104,186; Bobo, U.S. Pat. No. 3,112,800; Andersen, U.S. Pat. No. 3,203,736; Book, U.S. Pat. No. 3,326,607; Pittman, U.S. Pat. No. 3,331,456; Goodwin et al., U.S. Pat. No. 3,375,887; Goodwin et al., U.S. Pat. No. 3,419,220; Johnson, Jr., U.S. Pat. No. 3,528,704; Aarup, U.S. Pat. No. 3,536,151; Chaney, U.S. Pat. No. 3,554,602; Okabe, U.S. Pat. No. 3,572,839; and Taylor et al., U.S. Pat. No. 3,799,615.
Also known in the prior art are various devices for producing very high velocity pulsed liquid jets. One of the reasons for providing the pulsed jet is that relatively higher pressures are obtainable than would otherwise be possible with comparable apparatus for steady state flow. Typical of such devices are those shown in the following patents: Hansell, U.S. Pat. No. 2,512,743; Stanton, U.S. Pat. No. 2,665,052; Voitsekhovsky, U.S. Pat. No. 3,343,794; Cooley, U.S. Pat. No. 3,490,696; McDonald, U.S. Pat. No. 3,514,037; Cooley, U.S. Pat. No. 3,520,477; Cooley, U.S. Pat. No. 3,521,820; Cooley, U.S. Pat. No. 3,539,104; Abrams et al., U.S. Pat. No. 3,653,596; Beck, Jr., U.S. Pat. No. 3,704,966; Cobb et al., U.S. Pat. No. 3,729,137; Hall et al., U.S. Pat. No. 3,746,256; Godfrey, U.S. Pat. No. 3,748,953; and Cooley, U.S. Pat. No. 3,784,103. Representative of the prior art of patents showing another nozzle configuration is Franz, U.S. Pat. No. 3,750,961.
In recent years, there has been development work on high pressure intensifiers capable of producing a substantially constant discharge of a fluid jet stream at velocities in the order of 1,200 feet per second and substantially greater. Such a device is shown in U.S. Pat. No. 3,811,795. One of the practical applications of such a device is in jet cutting, in which a small diameter fluid jet (e.g. having a diameter between several hundreth to as small as several thousandths of an inch) is used to cut a relatively narrow kerf in a variety of materials, such as wood, fabric, sandstone, etc.
Usually this type of liquid jet cutting with a relatively small, very high velocity liquid jet is a reasonably precise operation, so that one of the major considerations is to avoid undue dispersion of the liquid jet, which stated positively is to provide a more "coherent" or "collimated" jet stream. The advantages of such a collimated jet stream are several, for example, cutting more efficiently, cutting a narrower kerf, having a better finish along the cut surfaces, avoiding undue wetting of the material being cut, etc. To the best knowledge of the applicant herein, most of the efforts to avoid dispersion of the jet have been directed toward improving the nozzle configuration and providing carefully contoured converging surfaces leading into the nozzle opening. One such approach is shown in U.S. Pat. No. 3,756,106 wherein is shown a corundum crystal of a particular configuration capable of producing a very high pressure liquid jet for relatively precise cutting operations, such as listed above. Thus, the main components of a prior art liquid jet cutting apparatus comprise a source of high pressure liquid, conduit means to carry the liquid to the area of cutting, and a carefully constructed and/or contoured nozzle assembly to receive the high pressure liquid from the conduit means and discharge this liquid as a small diameter, high velocity cutting jet.